In database systems, durability is the ACID property which guarantees that transactions that have committed will survive permanently.
For example, if a flight booking reports that a seat has successfully been booked, then the seat will remain booked even if the system crashes.

Durability can be achieved by flushing the transaction's log records to non-volatile storage before acknowledging commitment.

Many DBMSs implement durability by writing transactions into a transaction log that can be reprocessed to recreate the system state right before any later failure. A transaction is deemed committed only after it is entered in the log.